Optical fibers and/or optical fiber arrays may be connected to optoelectronic devices in the form of planar lightwave circuits (PLC). The alignment of such connections is important as it affects the quality of the transmitted optical signal (e.g., its intensity and/or insertion loss). Attaching optical fibers to PLC devices is a fundamental aspect of the manufacturing and assembly process. The accuracy with which this process is executed can affect the overall device performance. Present alignment methodologies for a multi-ported optical device require the simultaneous positioning, or alignment, of at least three independent physical units, in free space. The complexity of this scheme is significant in that each unit must have its own independent positioning system. The movement of each of the positioning systems must be orchestrated in such a manner that a line-of-sight, or optically conductive path, be established through all of the units.
A large class of products utilize PLC to fiber connections. These include both active and passive photonic components such as arrayed wave gratings, lasers, filters and amplifiers. Each of these components possesses input and output ports that convey light. The best way to properly direct light to and from these ports is to convey the light with a guided wave structure. This requires the use of optical fibers or optical fiber arrays. The nature of this operation is inherently complex and time consuming. At a minimum it requires the manipulation of at least two independent fibers, each with six degrees of freedom while trying to obtain levels of precision at the submicron level.
U.S. Pat. No. 5,926,594 describes an example of this methodology. Once the optical path is established, the units' positions must be secured and made permanent relative to the other units. This operation includes the application of a bonding material that must be cured through the application of infrared radiation or thermal energy. This type of curing process may impart stresses and relative displacement between the units as the state of the curing material changes. The displacement may include warping and twisting that will affect the planarity of the finished assembly. The finished assembly itself is affixed to a rigid substrate to increase its overall mechanical strength.
The prior art approach has several disadvantages. The approach is mechanically complex because it requires a six degree-of-freedom positioning mechanism for each of the three independent units. Further, the time required for the alignment process to converge to the optimal alignment is long and extended due to an unconstrained geometry and an inherently iterative, sequential process. Also, the optimal alignment for the assembly, which comprises a series of optical paths, is no better than the insertion loss of the optically worst path of the series of paths. For example, in trying to align eight parallel optical paths, one finds that the optimal position has 0 dB insertion loss on seven of the eight paths and that the eighth path has an insertion loss of 5 dB. Assuming that this is the best one can do, the so-called best path is limited by the path having the greatest insertion loss—the 5 dB path. That path represents the worst-case insertion loss path, which is an inseparable function of the alignment of all three units. Another issue is the accumulation of mechanical tolerances. By cascading all of the alignment parameters into a single operation, it is not possible to optimize sub-alignment tasks.
Therefore, there is a need for an improved method of aligning optical fibers and/or optical fiber array structures to optoelectronic devices.